It is well,known that whenever the amount of light entering the eye is reduced, the eye pupil dilates. Such dilation occurs when an individual enters into a dark room, and to a lesser extent when sunglasses are worn. In most people, when the pupil is dilated, the eye exhibits natural spherical aberration and reduced vision. Spherical aberration is caused by those light rays entering the periphery of the dilated pupil which otherwise do not enter the pupil when the same is constricted. When the pupil is dilated, these peripheral light rays focus too rapidly in a position which is often located in front of the retina, thus creating a condition of slight myopia (nearsightedness) and reducing distance vision. Individuals who have undergone refractive surgery such as radial keratotomy or excimer laser keratotomy typically experience an increased amount of spherical aberration as a result of the surgery and generally complain that they do not see well at night or when wearing sunglasses.
In recent years, improvements have been made in filtering harmful light rays by contouring sunglasses in a manner wherein they wrap around the wearer's face. Such wrapping places the protective lenses of the sunglasses closer to the wearer's eyes, particularly temporally, and reduces the amount of peripheral unfiltered light which enters the eyes. The increasing popularity of wrap around sunglasses is not only attributable to the greater shielding of the eyes they provide, but to their styling and the athletic image connoted thereby.
Though wrapping sunglasses about the wearer's face enhances peripheral vision and provides better side protection to the eyes, such wrapping creates optical distortion referred to as base-out prism. It has been found that increased amounts of unwanted base-out prism are induced when the lenses of the wrap around sunglasses have steeper lens curves and higher refractive indexes.
The present invention overcomes the above-described deficiencies of prior art wrap around sunglasses. In accordance with the present invention, there is provided wrap around sunglasses which include lenses having a small amount of negative lens power to decrease spherical aberration caused by the sunglasses. The sunglasses of the present invention are configured such that these negative powered lenses are provided with optical centers which are decentered temporally for purposes of inducing base-in prism that neutralizes the wrap induced base-out prism. Importantly, the small amount of negative lens power provided in the lenses is within the lens power tolerance of the American National Standards Institute for over-the-counter sunglasses.